The present invention pertains to a ceramic cutting tool, and a composition thereof, that has whisker reinforcement. More specifically, the invention pertains to a ceramic cutting tool, and a composition thereof, that has ceramic whisker reinforcement wherein at least 50 volume percent of the ceramic matrix comprises a carbide, nitride and/or carbonitride of titanium, hafnium, molybdenum, zirconium, tantalum, niobium, vanadium and/or tungsten.
In the past, there have been ceramic bodies with whisker reinforcement such as that disclosed in U.S. Pat. No. 4,543,345 to Wei. The Wei Patent discloses an alumina matrix with silicon carbide whisker reinforcement, a boron carbide matrix with silicon carbide whiskers, and a mullite matrix with silicon carbide whiskers. According to the Wei patent, the incorporation of silicon carbide whiskers increased the fracture toughness of the substrate.
Japanese Publication No. 63-10758 to Yamagawa et al. pertains to a ceramic composite that comprises alumina as its main component. The balance comprises between 5 to 40 weight TiC and 2 to 40 weight percent silicon carbide whiskers. The combined amount of titanium carbide and silicon carbide whiskers cannot exceed 50 weight percent, i.e., it is 50 weight percent or less. This document also mentions that there can be up to 10 weight percent of an oxide, carbide or nitride of aluminum, silicon and the Group IVa, Va and VIa elements.
U.S. Pat. No. 4,507,224 to Toibana et al. makes general reference to certain nitrides and carbides as suitable matrix material, along with electroconductive powder, for SiC fiber reinforcement. The SiC fibers are present in an amount between 5 and 50 weight percent. The '224 patent makes specific reference to matrices of silicon nitride, aluminum nitride, boron nitride, silicon carbide, boron carbide, and titanium carbide. The '224 Patent recites examples that use alumina, zirconium oxide, silicon nitride as matrices along with silicon carbide fibers. The focus of the '224 Patent is on a ceramic article suitable for electric discharge machining. In this regard, the specification states that the electrical resistance of the substrate must not exceed 10 ohm-cm The publication "Fiber Reinforced Ceramics: A Review and Assessment of their Potential" by Kpochmal (at pages 9 through 16) mentions ceramics (with fiber reinforcement) having a HfC or ZrC matrix. The filaments include tungsten, molybdenum, tantalum, boron, carbon, silicon carbide, boron carbide, and alumina.
There have also been ceramic cutting tools with whisker reinforcement. In this regard, U.S. Pat. No. 4,789,277 to Rhodes et al. discloses the use of ceramic whiskers (the content ranges from 2 volume percent to 40 volume percent) such as alumina, aluminum nitride, beryllia, boron carbide, graphite, silicon carbide (preferably), and silicon nitride in a ceramic matrix. The ceramic matrix is preferably alumina, but includes alumina "doped" with up to 30% zirconia, hafnia and titanium carbide. The alumina remains the dominant component of the matrix.
PCT.backslash.US 86.backslash.00528 Patent Application to Rhodes et al. entitled HIGH DENSITY REINFORCED CERAMIC BODIES AND METHOD OF MAKING SAME has as its focus the pressureless sintering of whisker-reinforced ceramic bodies. This document mentions a whisker content of between 0.5 and 21 volume percent. The specific examples teach the use of an alumina matrix with SiC whisker contents from 6.1 volume percent to 29.2 volume percent.
U.S. Pat. No. 5,059,564 to Mehrotra et al. for an ALUMINA-TITANIUM CARBIDE-SILICON CARBIDE COMPOSITION pertains to an alumina-based matrix containing a dispersion of SiC whiskers and a TiC phase. The SiC whiskers comprise 1.0 to less than 30 volume percent with the most preferred range being 2.5 to 20 volume percent. The TiC comprises 5 to 40 volume percent, and preferably, with up to 3 volume percent of a sintering aid residue.
U.S. Pat. No. 5,427,987 to Mehrotra et al. for a GROUP IVB BORIDE BASED CUTTING TOOLS FOR MACHINING GROUP VIB BASED MATERIALS concerns zirconium boride, hafnium boride and especially titanium boride cutting tools. The addition of W and Co to the boride powder improves the densification of the composition.
The 1969 Air Force Report by Whitney et al. mentions the use of a generally high content of particle reinforcement in ZrN and HfN matrices for use as cutting tools. In this 1969 Report there is no suggestion that whiskers could reinforce these matrices.
U.S. Pat. No. 5,231,060 to Brandt teaches using whiskers of the nitride, carbides and borides of Ti, Zr, Hf, V, Nb or Ta to reinforce an oxide-based matrix such as alumina for use as a cutting tool.
U.S. Pat. No. 5,439,854 to Suzuki et al. pertains to a cutting tool that contains 40 weight percent or more of TiC, and 5 to 40 weight percent of silicon carbide whiskers (of a length equal to 20 micrometers or less). The cutting tool may also contain up to 40 weight percent alumina, as well as sintering aids. Up to 40 weight percent of the TiC may be substituted by Ti or a Ti-based compound such as a nitride, boride, or oxide.
Table I set forth below presents certain physical properties of some prior art commercial cutting tools.
TABLE I Selected Physical Properties of Certain Commercial Cutting Tools VHN (GPa) [18.5 kg K.sub.IC (E&C) Cutting Tool HRA load] [MPam.sup.1/2 ] WG-300 94.6 19.4 6.1 HC6 94.6 19.4 5.1 K090 94.8 19.1 4.7
Referring to these commercial cutting tools, the WG-300 cutting tool is sold by Greenleaf Corporation of Saegertown, Pennsylvania and has a composition of about 25 volume percent SiC whiskers and the balance alumina. The HC6 cutting tool is sold by NTK Cutting Tool Division of NGK Spark Plugs (U.S.A.), Inc. of Farmington Hills, Mich., and has a composition of about 70 weight percent TiC and the balance alumina. The K090 cutting tool is made by Kennametal Inc. of Latrobe, Pa. and has a composition of about 70 volume percent alumina and 30 volume percent TiC. Each of these compositions may also contain minor amounts of sintering aid.